Mechanisms Underlying the Strong Inhibition of Muscle-Type Nicotinic Receptors by Tetracaine

Nicotinic acetylcholine (ACh) receptors (nAChRs) are included among the targets of a variety of local anesthetics, although the molecular mechanisms of blockade are still poorly understood. Some local anesthetics, such as lidocaine, act on nAChRs by different means through their ability to present as both charged and uncharged molecules. Thus, we explored the mechanisms of nAChR blockade by tetracaine, which at physiological pH is almost exclusively present as a positively charged local anesthetic. The nAChRs from Torpedo electroplaques were transplanted to Xenopus oocytes and the currents elicited by ACh (I_ACh s), either alone or co-applied with tetracaine, were recorded. Tetracaine reversibly blocked I_ACh , with an IC₅₀ (i.e., the concentration required to inhibit half the maximum I_ACh ) in the submicromolar range. Notably, at very low concentrations (0.1 μM), tetracaine reduced I_ACh in a voltage-dependent manner, the more negative potentials produced greater inhibition, indicating open-channel blockade. When the tetracaine concentration was increased to 0.7 μM or above, voltage-independent inhibition was also observed, indicating closed-channel blockade. The I_ACh inhibition by pre-application of just 0.7 μM tetracaine before superfusion of ACh also corroborated the notion of tetracaine blockade of resting nAChRs. Furthermore, tetracaine markedly increased nAChR desensitization, mainly at concentrations equal or higher than 0.5 μM. Interestingly, tetracaine did not modify desensitization when its binding within the channel pore was prevented by holding the membrane at positive potentials. Tetracaine-nAChR interactions were assessed by virtual docking assays, using nAChR models in the closed and open states. These assays revealed that tetracaine binds at different sites of the nAChR located at the extracellular and transmembrane domains, in both open and closed conformations. Extracellular binding sites seem to be associated with closed-channel blockade; whereas two sites within the pore, with different affinities for tetracaine, contribute to open-channel blockade and the enhancement of desensitization, respectively. These results demonstrate a concentration-dependent heterogeneity of tetracaine actions on nAChRs, and contribute to a better understanding of the complex modulation of muscle-type nAChRs by local anesthetics. Furthermore, the combination of functional and virtual assays to decipher nAChR-tetracaine interactions has allowed us to tentatively assign the main nAChR residues involved in these modulating actions.

[CONTEMPORARY APPROACH TO DIAGNOSIS OF SUBCLINICAL HEART FAILURE]

Treatment of congestive heart failure (CHF) remains one of the challenging problems in cardiology. In recent years, the method of multifrequency bio-impendancemetry is used in patients with CHF for the assessment of water imbalance and determination of its severity. The aim of the study was to determine the diagnostic capabilities of bio-impendancemetry in evaluation of the early manifestations of CHF. The study included 92 healthy individuals, and 335 patients who were hospitalized in the cardiology department with NYHA I-II functional class (FC) of chronic CHF. The echocardiography, rheography and biochemical examination were performed for determination of FC of CHF. Procedures were repeated at day 5 of hospitalization, 6-minute walk test was performed to assess physical tolerance and objectification of the functional status of patients with CHF. 45 patients had signs of CHF FC III-IV, therefore, they were excluded from the study. Analysis of endpoints was conducted by telephone survey in 1 year after discharge from the hospital. The results of the comparison of the predictive value of different methods for diagnosing CHF showed maximum sensitivity for brain natriuretic peptide (BNP) which was 82%, specificity was 88%. The 6-minute walk test showed the lowest values of sensitivity and specificity (sensitivity 67%, specificity 72%) as well as leg impedance at low frequencies (LF) (sensitivity 69%, specificity 74%). The values for the leg impedance at high frequencies (HF) were as follows: sensitivity 68%, specificity 97%. High predictive value of a positive result (PPV) was shown in phase angle (91%) and BNP (91%). Left ventricle ejection fraction(LVEF) measurements had the lowest PPV (72%).

alpha-fetoprotein causes apoptosis in tumor cells via a pathway independent of CD95, TNFR1 and TNFR2 through activation of caspase-3-like proteases

alpha-Fetoprotein (AFP) is an oncoembryonal protein with multiple cell growth regulating, differentiating and immunosuppressive activities. Previous studies have shown that treatment of tumor cells in vitro with 1-10 microM AFP produces significant suppression of tumor cell growth by inducing dose-dependent cytotoxicity, but the molecular mechanisms underlying these AFP functions are obscure. Here, we show that AFP cytotoxicity is closely related to apoptosis, as shown by cell morphology, nuclear DNA fragmentation and caspase-3-like activity resulting in cleavage of poly(ADP-ribose) polymerase. Apoptosis was significantly inhibited by a CPP32 family protease inhibitor whereas a general caspase inhibitor had no inhibitory effect, showing some enhancement of AFP-mediated cell death. Using fluorogenic caspase substrates, we found that caspase-3-like proteases were activated as early as 4 h after treatment of Raji cells with 15 microM AFP, whereas caspase-1, caspase-8, and caspase-9-like activity was not detected during the time interval 0.5-17 h. AFP treatment of Raji cells increased Bcl-2 protein, showing that AFP-induced apoptosis is not explained by downregulation of the Bcl-2 gene. This also suggests that AFP operates downstream of the Bcl-2-sensitive step. AFP notably decreased basal levels of soluble and membrane-bound Fas ligand. Incubation of AFP-sensitive tumor cells (HepG2, Raji) with neutralizing anti-Fas, anti-tumor necrosis factor receptor (TNFR)1 or anti-TNFR2 mAb did not prevent AFP-induced apoptosis, demonstrating its independence of Fas-dependent and TNFR-dependent signaling. In addition, it was found that cells resistant to TNF-induced (Raji) or Fas-induced (MCF-7) apoptosis are, nevertheless, sensitive to AFP-mediated cell death. In contrast, cells sensitive to Fas-mediated cell death (Jurkat) are completely resistant to AFP. Taken as a whole, our data demonstrate that: (a) AFP induces apoptosis in tumor cells independently of Fas/Fas ligand or TNFR/TNF signaling pathways, and (b) AFP-mediated cell death involves activation of the effector caspase-3-like proteases, but is independent of upstream activation of the initiator caspase-1, caspase-8, and caspase-9-like proteases.

[A rare case of an adenomatoid mesothelioma of the fallopian tube combined with ovarian stromal hyperplasia and hyperthecosis, endometrial adenocarcinoma and endometriosis interna]

Adenomatoid mesothelioma is a rare benign tumor, most commonly located in the uterine corpus and fallopian tubes in the women during the reproductive years. It usually occurs occasionally and there are no specific symptoms. A case is presented of an adenomatoid tumor of the fallopian tube, associated with many other pathological findings of the genital tract. It is important to recognize the pseudoglandular pattern of this rare kind of benign tumor to avoid a mistaken diagnosis of adenocarcinoma or metastasis.

C-reactive protein-like immunoreactivity in the neurofibrillary tangles of Alzheimer's disease

C-reactive protein (CRP) is a plasma acute-phase protein, normally not found in the brain. Previous studies have demonstrated the presence of CRP in the senile plaques of Alzheimer's disease (AD). In this study, the presence of CRP-like immunoreactivity in AD neurofibrillary tangles (NFT) was demonstrated following pre-treatment of tissue sections with formic acid. CRP-like immunoreactivity was observed in both extracellular and intracellular NFT and was co-localized with the NFT marker PHF-1 and the amyloid P component (AP). The CRP-like immunoreactive NFT were less numerous and more limited in their distribution than PHF-1 or AP-immunoreactive NFT. The present results further support an involvement of inflammatory processes in the etiology of AD.